1. Field of the Invention
The present invention relates to a semiconductor device, a film used for manufacturing such a semiconductor device and manufacturing methods for the device and the film.
2. Description of the Related Art
Recently, semiconductor elements are very densely packaged. Accordingly, there is a demand for a semiconductor device having a large number of connection pins. As a semiconductor device suitable for packaging semiconductor elements very densely on a surface at low cost, the ball grid array (BGA) structure type semiconductor device has been investigated for practical use. Compared with a conventional semiconductor device, such as the quad flat package (QFP), the ball grid array structure is advantageous in that a large number of external connecting terminals can be arranged without increasing the density of lead arrangement, so that the yield is high in the actual packaging process.
However, in the conventional ball grid array structure type semiconductor device, the following problems may be encountered. Due to a difference between the thermal expansion coefficient of a mount substrate and that of a package substrate, a thermal stress is caused. Cracks are caused on the package substrate by this thermal stress and, further, the package substrate is deformed.
Usually, a substrate made of glass-epoxy is used for the mount substrate of the semiconductor device. The thermal expansion coefficient of the glass-epoxy substrate is approximately 15.times.10.sup.-6 /.degree. C. For example, when the package substrate is made of alumina ceramics, the thermal expansion coefficient is approximately 7.times.10.sup.-6 /.degree. C. When the package substrate is made of aluminum nitride ceramics, the thermal expansion coefficient is approximately 4.times.10.sup.-6 /.degree. C. As described above, compared with the thermal expansion coefficient of the mount substrate, the thermal expansion coefficient of the package substrate is very small. Therefore, when ceramics are used for the package substrate, the thermal stress caused between the mount substrate and the semiconductor device cannot be neglected (i.e., ignored).
On the other hand, when plastics are used for the material of the package substrate, the thermal expansion coefficient of the package substrate can be made approximately the same as that of the actual packaging substrate. Due to the foregoing, both thermal expansion coefficients can be matched to each other. In this case, however, when the thermal expansion coefficient of the semiconductor chip is compared with the thermal expansion coefficient of the package substrate, the thermal expansion coefficient of the package substrate is much higher than that of the semiconductor chip. Accordingly, the thermal stress caused between the package substrate and the semiconductor chip is increased. Such a thermal stress becomes one of the problems.
Further, the following problems may be encountered. Since plastics are flexible to some extent, the package substrate is warped badly by the shrinkage caused in the process of resin molding. Furthermore, when plastics are used for the semiconductor device, the heat dissipation property is generally low. In order to solve the above problems, it is possible to employ a package substrate having a metallic core. However, when this type package substrate is employed, the manufacturing cost is very high.
In this connection, as a low cost surface mount type semiconductor device there is provided a tape carrier package (TCP). This is a simple semiconductor device composed in such a manner that a semiconductor chip is connected with a TAB tape and the semiconductor chip is sealed by means of potting. However, this TCP is disadvantageous in that the leads are easily deformed, so that the product is difficult to handle. In order to solve the above problem, the semiconductor chip is sealed in a wide area by means of potting, or alternatively, resin molding is conducted so as to provide a shape preserving property. However, this method is disadvantageous in that the heat dissipation property of the semiconductor device is deteriorated.